The present invention relates to electronic systems having card cages for printed wiring cards and, more particularly, to such systems having retainer bars to retain the printed wiring cards within their card cages.
A card cage may be used in an electronic system to hold printed wiring cards. Where they are used, card cages have a number of locations for cards that are commonly referred to as slots because of slotted guides that guide the cards into and out of their mating connectors. One (sometimes more) of the mating connectors are located at the bottom of each slot (if the cards are accessed from the top) or at the back (if the cards are accessed from the front). Each printed wiring card is inserted into its slot with enough force to insert the connector pins or conductors at the back of the printed wiring card into physical and electrical connection with its respective mating connector at the back or the bottom of the slot, as the case may be. The mating connectors have spring elements in each of their pin or conductor receptacles that are usually forced into tension by the insertion of its mating pin or conductor from the printed wiring card. Once the pins or conductors have been inserted into their respective receptacles, friction between the pins or conductors and their receptacles, as well as friction between the sides of the slot against the sides of the card, will usually hold the cards in the inserted position.
If the electronic system is subjected to periods of vibration, however, one or more of the printed wiring cards may be vibrated loose from its inserted position. If a printed wiring card is vibrated loose, the problem is that some of the same friction that held the card in position will now work against the card's return to the inserted position. Additionally, the force needed to re-insert pins or conductors that have vibrated loose from their spring tensioned receptacles typically can only be supplied by a human operator.